Drug-induced erythema multiforme: a possible immunologic pathogenesis.

A 37-year-old female developed erythema multiforme 17 days after beginning carbamazepine for complex partial seizures. The carbamazepine was discontinued and phenytoin begun. A new rash developed and phenytoin therapy was stopped. In vitro immunologic studies were conducted in an effort to understand the pathogenesis of the rashes. Enhancement of stimulated in vitro lymphocyte proliferation from the patient occurred in the presence of carbamazepine and phenytoin. Neither drug had an enhancing effect on lymphocyte proliferation from a control subject. These data, together with clinical data, strongly suggest an immunologic pathogenesis for drug-induced erythema multiforme.